Universal Mobile Telecommunications System (UMTS) is an example of a mobile radio communications system. UMTS is a 3rd Generation (3G) mobile communication system employing Wideband Code Division Multiple Access (WCDMA) technology standardized within the 3rd Generation Partnership Project (3GPP). In the 3GPP release 99, the radio network controller (RNC) in the radio access network controls radio resources and user mobility. Resource control includes admission control, congestion control, and channel switching which corresponds to changing the data rate of a connection. Base stations, called node Bs (NBs), which are connected to an RNC, orchestrate radio communications with mobile radio stations over an air interface. The RNC controls what system information the Node B should broadcast and is the control plane protocol termination point towards the user equipments (UEs). RNCs are also connected to nodes in a core network. i.e., Serving GPRS Support Node (SGSN), Gateway GPRS Support Node (GGSN), mobile switching center (MSC), etc. Core network nodes provide various services to mobile radio users who are connected by the radio access network such as authentication, call routing, charging, service invocation, and access to other networks like the Internet, public switched telephone network (PSTN), Integrated Services Digital Network (ISDN), etc.
FIG. 1 illustrates an example UMTS system 1 in which UMTS Terrestrial Radio Access Network (UTRAN) 4 is coupled to a core network 3 via an Iu interface and communicates over an air Uu interface with mobile terminals called user equipments (UEs) 8. The core network includes core network nodes like mobile switching centers (MSCs) and Serving GPRS Support Nodes (SGSNs) that interface with other networks the Internet, public switched telephone network (PSTN), Integrated Services Digital Network (ISDN), etc. 2. The UTRAN 4 includes radio network systems (RNSs) 5 that each include an RNC 6 coupled to one or more Node B base stations 7 over an Iub interface. Different RNCs 6 communicate information over and Iur interface. Each Node B 7 coordinates coverage and communication in one or more cells. In the example, each Node B is associated with three cells. From the UE's point of view, an RNC may be a Serving RNC that terminates the UE's link layer communications. From the core network point of view, the Serving RNC terminates the Iu interface for this UE. The Serving RNC also exerts admission control for new mobiles or services attempting to use the core network over its Iu interface. Admission control ensures that UEs are only allocated radio resources (e.g., bandwidth and signal/noise ratio) up to what the network has available. An RNC can be a Drift RNC, where the UE's physical layer communications terminate in a soft handover situation where the UE has moved from a cell associate with the serving RNC and moved to a cell associated with another, drift RNC. The Drift RNC communicates with the Serving RNC via the Iur interface.
The Long Term Evolution (LTE) of UMTS is under development by the 3rd Generation Partnership Project (3GPP) which standardizes UMTS. There are many technical specifications hosted at the 3GPP website relating to Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN), e.g., 3GPP TS 36.300. The objective of the LTE standardization work is to develop a framework for the evolution of the 3GPP radio-access technology towards a high-data-rate, low-latency and packet-optimized radio-access technology. In particular, LTE aims to support services provided from the packet switched (PS)-domain. A key goal of the 3GPP LTE technology is to enable high-speed packet communications at or above about 100 Mbps.
FIG. 2 illustrates an example of an LTE type mobile communications system 10. An E-UTRAN 12 includes E-UTRAN NodeBs (eNBs) 18 that provide E-UTRA user plane and control plane protocol terminations towards the user equipment (UE) terminals 20 over a radio interface. The eNB controls radio resources and user mobility. An eNB is sometimes more generally referred to as a base station, and a UE is sometimes referred to as a mobile radio terminal or a mobile station. As shown in FIG. 2, the base stations are interconnected with each other by an X2 interface. The base stations are also connected by an S1 interface to an Evolved Packet Core (EPC) 14 which includes a Mobility Management Entity (MME) and to a System Architecture Evolution (SAE) Gateway. The MME/SAE Gateway is shown as a single node 22 in this example and is analogous in many ways to an SGSN/GGSN gateway in UMTS and in GSM/EDGE. The S1 interface supports a many-to-many relation between MMEs/SAE Gateways and eNBs. The E-UTRAN 12 and EPC 14 together form a Public Land Mobile Network (PLMN). The MMEs/SAE Gateways 22 are connected to directly or indirectly to the Internet 16 and to other networks.
A cellular network operator sometimes needs to restrict access by UEs to one or more cells in its network. There are three categories of restrictions including barring a cell, reserving a cell for operator use, and reserving a cell for use by only UEs having certain “access classes”. A barred cell is a cell that a UE is not allowed to camp on. A reserved cell is a cell on which camping is not allowed, except for particular UEs, if so indicated in the system information. A restricted cell is a cell on which camping is allowed, but access attempts are disallowed for UEs whose associated access classes are indicated as barred. In all of these cases, the cell is considered restricted in some way.
A significant problem created with restricted cells is how to communicate to other RAN nodes, e.g., eNBs in an LTE system, that such a cell has changed its restriction status and that access to that cell for handovers, new connections, etc. is now available. One possible solution to this problem is to wait for a UE-specific message to be generated relating to the once restricted cell and include information in that UE-specific message indicating that the restricted cell is no longer restricted. But the disadvantage in this approach is that there may elapse significant time before such a UE-specific message is generated causing undesirable delay in that newly-unrestricted cell providing service. Moreover, there may be situations where because of cell restrictions, UE-specific handover messages are not allowed between the involved eNBs, which means that the restrictions might not even be lifted using UE-specific messages, requiring some sort of manual intervention by the operator.
On the other side of this issue is the related problem of promptly informing other eNBs of the restricted state of cell. In that case, unnecessary handover attempts may be made to the restricted cell that fail leading potentially to dropped connections. It also leads to higher signaling because another target cell must be selected for handover after the handover attempt fails and a new handover request is made towards this new target cell.
Another problem with UMTS and LTE systems is insufficient use of Access Control to prevent selected classes of UEs from sending initial access messages to restricted cells. At a user subscription, one or more Access Classes are allocated to the subscriber's UE and stored in the UE's Subscriber Identity Module (SIM). This access class information has the potential to be very useful to informing radio access nodes, like RNCs in UMTS and eNBs in LTE, about the cell restriction status of a large number of UEs. But so far that access class information is not systematically and efficiently provided to those radio access nodes.
It would also be desirable for LTE and UMTS networks to be able to use access class information to steer handovers towards the most appropriate frequency or Radio Access Technology (RAT) to assure that the UE receives good service in the target handover cell. To enable the network to steer handovers based on UE access class and access restriction in neighbor cells, the access class of the UE must be provided from the old serving RAN node to the new serving RAN node whenever there is a change of serving RAN node for a UE in an active state. In LTE, this means forwarding the access class at handover, and in UMTS, at Serving RNC (SRNC) relocation.
Depending on the cell restriction status emergency calls may or may not be allowed in the cell. An area restriction concept would restrict idle and active state UE access in tracking and location areas or even in PLMNs and entire RATs. A UE is only allowed to perform emergency calls in these areas or networks. But these areas are rather large, and sometimes it would be desirable to have the ability to restrict every thing except emergency calls on an individual cell level. Unfortunately, there is a lack of knowledge in a new serving RAN node whether a radio bearer is available for a particular UE's emergency call in a cell controlled by that new serving RAN node after changing from the old serving RAN node to the new serving RAN node.